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Re: (long) Top level heaps/subheaps

From: Tanel Poder <>
Date: Tue, 06 Jan 2004 08:04:26 -0800
Message-ID: <>

Well, a heap is just a bunch of memory (allocated in contiguous extents) and you can practically allocate any size of chunk of memory from it (with some restrictions). A regular heap has freelist and LRU list mechanisms for managing space in it as well as memory allocation/releasing routines which you can then call. Oracle uses its generic heap manager code (KGH) for managing it's memory.

Once you allocate a chunk from heap it's up to the allocator what he does with it. It can just use it for some kind of static data, but can also create another heap in these chunks it allocated, this heap may use different heap manager code for managing its memory if needed (for example shared pool reserved area and large pool behave a little differently, they don't have LRU list mechanisms).
If you take any heapdump using alter session set events 'immediate trace name heapdump level x' ; then top level heaps show parent=00000000 in their descriptors. Note that this "top call heap" has allocated chunks for heap with descriptor address 06B51DB0 (callheap) and also you see that "callheap" has a parent heap with descriptor address 06B52790.
HEAP DUMP heap name="top call heap"  desc=06B52790
 extent sz=0x213c alt=92 het=32767 rec=0 flg=2 opc=2
 parent=00000000 owner=00000000 nex=00000000 xsz=0xfffc
EXTENT 0 addr=071D0004
  Chunk  71d000c sz=      112    perm      "perm           "  alo=112
  Chunk  71d007c sz=    65412    free      "               "
EXTENT 1 addr=07170004
  Chunk  717000c sz=      232    perm      "perm           "  alo=232
  Chunk  71700f4 sz=    60724    free      "               "
  Chunk  717ee28 sz=     1352    freeable  "callheap       " 
  Chunk  717f370 sz=     1072    freeable  "callheap       "  ds=06B51DB0
  Chunk  717f7a0 sz=     1072    recreate  "callheap       "  latch=00000000
     ds  6b51db0 sz=     3496 ct=        3

HEAP DUMP heap name="callheap"  desc=06B51DB0
 extent sz=0x424 alt=32767 het=32767 rec=0 flg=2 opc=3
 parent=06B52790 owner=00000000 nex=00000000 xsz=0x53c
EXTENT 0 addr=0717EE34
  Chunk  717ee3c sz=     1332    freeable  "qkkele         "
EXTENT 1 addr=0717F37C
  Chunk  717f384 sz=      572    perm      "perm           "  alo=388
  Chunk  717f5c0 sz=      444    free      "               "
  Chunk  717f77c sz=       36    freeable  "qkkkey         "
EXTENT 2 addr=0717F7BC
  Chunk  717f7c4 sz=       28    perm      "perm           "  alo=28
  Chunk  717f7e0 sz=      956    free      "               "
  Chunk  717fb9c sz=       52    freeable  "event string   "
Total heap size    =     3420
 Bucket 0 size=76
 Bucket 1 size=268
  Chunk  717f7e0 sz=      956    free      "               "
  Chunk  717f5c0 sz=      444    free      "               "
 Bucket 2 size=1036
Total free space   =     1400
  Chunk  717f384 sz=      572    perm      "perm           "  alo=388
  Chunk  717f7c4 sz=       28    perm      "perm           "  alo=28
Permanent space    =      600

If making these "full" heapdumps puts too much strain on your system, then it might be easier to use event HEAPDUMP_ADDR which allows to dump heaps only with specified descriptor address. There are other options as well, such is X$KSMHP table to query any heap (which is, blah, highly unsupported) or attaching directly to SGA shared memory segment and reading from there.
Sorry for too long post, I'm currently too lazy to do anything useful...

----- Original Message -----
From: Sultan Syed
To: Multiple recipients of list ORACLE-L
Sent: Tuesday, January 06, 2004 3:49 PM
Subject: Top level heaps/subheaps

I am getting little confussion how the memory is allocated for
top-level heaps and subheaps in shared pool.

How can we know what are all the top-level heaps and subheaps and their hierarchy.
Is it possible to get it from any X$ tables.

Freeable chunks can be flushed out?If yes ,then why there should be another type as recreatable chunks?
Please explain.

Thanks in advance
Please see the official ORACLE-L FAQ:
Author: Tanel Poder

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Received on Tue Jan 06 2004 - 10:04:26 CST

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